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Nowadays multiple wireless communication systems operate in industrial environments side by side. In such an environment performance of one wireless network can be degraded by the collocated hostile wireless network having higher transmission power or higher carrier sensing threshold. Unlike the previous research works which considered IEEE 802.15. 4 for the Industrial Wireless communication systems (iWCS) this paper examines the coexistence of IEEE 802.11 based iWCS used for delay-stringent communication in process automation and gWLAN (general-purpose WLAN) used for non-real time communication. In this paper, we present a Markov chain-based performance model that described the transmission failure of iWCS due to geographical collision with gWLAN. The presented analytic model accurately determines throughput, packet transaction delay, and packet loss probability of iWCS when it is collocated with gWLAN. The results of the Markov model match more than 90% with our simulation results. Furthermore, we proposed an adaptive transmission power control technique for iWCS to overcome the potential interferences caused by the gWLAN transmissions. The simulation results show that the proposed technique significantly improves iWCS performance in terms of throughput, packet transaction, and cycle period reduction. Moreover, it enables the industrial network for the use of delay critical applications in the presence of gWLAN without affecting its performance.